This invention relates to a control valve for a brake booster having a control valve that restricts the flow of fluid from an inlet port past a seat to an outlet port during a brake application and a shroud on the control valve that deflects the flow of fluid from impinging on a return spring to attenuate the development of a reaction in the return spring that may create an undesirable audible noise.
The structural components in hydraulic —Hlt429300206—Hlt429300206 brake boosters, such as illustrated in U.S. Pat. No. 4,961,846, are designed to permit fluid under pressure in a fluid supply system to continually flow from an inlet port through a power piston to an outlet port when in an inactive or rest position. In actuation position, an input force applied to a control valve moves the control valve toward a valve seat in the power piston to restrict the flow of fluid present in an inlet chamber and create a fluid pressure differential across the power piston. After overcoming a return spring, the pressure differential acts on and moves the power piston to develop an output force. When the control valve is in the rest position, fluid freely flows through the power piston and creates an essentially broad band non-reaction sound. This broad band non-reaction sound is combined with noises produced by the engine and other components in a vehicle and is accepted as a total overall operational sound of the vehicle. When the flow of fluid through the power piston is restricted, a corresponding resonant frequency is created by the flow of fluid to the outlet port that is manifested as an undesirable noise or audible resonant sound. U.S. Pat. No. 6,170,381 discloses the use of a labyrinth seal that is located on a face of the control valve to modify or change the frequency created by fluid flowing past the seat to the outlet port. However, in further evaluation of brake boosters it was discovered that other factors and structural relationships including the effect of flowing fluid acting on the return spring caused a reaction that produced a whistle as the fluid flows to the outlet port during a brake application.